
Why is en passant only possible in the next move?



Somebody mentioned, "Why can't the pawn capture a bishop in passing?" perhaps somewhat in jest. The answer is that en passant capture is a special rule covering moves that are deviations from the norm.
Also confusing for some beginners is the fact that the king cannot pass through a pawn's attack when castling. Again, it's because castling is another of the rules that are deviant, made in the interest of modernizing the game and speeding up the action a wee bit.
A-ha, so a king can be captured en-passant, by any peice including a pawn. Bascially any peice that can normally only move one square in the event that a "special move" allows it to move more than one square. (Which is why a rook can't be captured en-passant during castling?)

OK, why this ability is limited to only capturing pawns while in passing, then I just don't know. If a rook or a queen traverses a capture square of one of my pawns why can't I catpure it similarly?
Chess would become a much more dynamic game that way.

Joking? No, a king can't be captured en passant, as the rules prevent its passing. Otherwise, yes, it could, and of course, the only pieces that move only one square unless a special rule allows it to move two are the king and the pawn.
Well yes, but a simple extension of the principle. A king normally can't move into check (nor can a move be played that allows it to remain in check). The can't move through check is clearly in recognition of the en-passant principle.

Howcome a pawn cannot capture on the 4th rank while on their first move to pre-empt en-passant? Rather than moving to the square beside the enemy pawn you could take it (resulting in a move identical to a knight's).

Because the god of chess, Caissa, created chess that way.
If you disobey her rules, you will be sent to chess hell where you play for eternity and lose every game to your dog.

Or your cat, as the case may be. Or you constanly lose simuls against every pet you've ever had. Even the hamsters.

Ziryab, you've got it backwards. The pawn is what would be subject to capture if an enemy piece controlled the third rank as it leapt to the fourth.
I'm too old too learn this stuff. Let's just keep the rules perfect as g-d intended. The rules crafted during the Inquisition are as near perfect as possible, especially with the nineteenth century European imperial expectation that White moves first.

I figured this was just so we won't have to remember and keep track of which pawns are "in passing" and which aren't. it makes sense to remember what just happened but otherwise it's not visible on yhe board anywhere. a better q. is why only pawns can do it. or, can we just get rid of it? do we really need e.p. anymore?